The present invention relates to a rear wheel steering system applied to motor vehicles, and more particularly, to improvements in the construction of the steering system.
Recently, various systems for steering the rear wheels have been proposed with the object to improve the cornering performance or the cornering radius of a motor vehicle.
A conventional rear wheel steering system disclosed, for example, in Japanese Patent Disclosure No. 179369/85 is applied with the same construction as is in a front wheel steering system. More particularly, this type has an acutator for steering the rear wheels, a knuckle rotatably provided at a vehicle body for supporting the rear wheels, and a tie rod coupling the actuator and the knuckle for transmitting the movement of the actuator to the knuckle, thereby steering the rear wheels.
However, the conventional steering system which employs such a rotatable knuckle has the drawbacks in which a McPherson strut type suspension for rear wheels or double Wishbone type suspension for rear wheels, must be utilized which has a complicated structure thus necessitate a large space and an increased cost. Further, since this conventional system should further avoid the link interference between a suspension arm and a tie rod, it has another drawback that an ideal rear wheel suspension cannot be accomplished. A conventional rear wheel steering system which has a relatively simple structure for eliminating the above-mentioned drawback is disclosed, for example, in Japanese Patent Disclosure No. 99470/82. This steering system having a semi-trailing arm type suspension for rear wheels forcibly deforms a bushing for supporting a cross member to a vehicle body by an actuator to thereby incline the cross member and the semi-trailing arm, thereby steering a rear wheel.
However, since this steering system employs the semi-trailing arm type suspension, a laterial force acting on the rear wheel is input from a suspension arm through the cross member to the bushing. Thus, since this system needs to flexibly set the bushing so as to perform the rear wheel steering, if the hydraulic system of the actuator fails, the bushing is largely deformed by a lateral force input from the road surface to the rear wheel during cornering of the vehicle, so that the semitrailing arm and the cross member incline with the result that so-called "a compliance steering phenomenon" for steering the rear wheels in the reverse direction to the front wheels feasibly increases to cause an over-steering to occur, thereby deteriorating steering stability. Thus, the conventional steering system has drawbacks which largely deteriorate the function as a suspension when the hydraulic system fails.
Further, since the conventional rear wheel steering system inclines the entire rear wheel suspension arrangement with respect to a vehicle body, the system has another drawback in that it requires a relatively high output actuator of large size and high cost.
Moreover, since the steering system deforms the bushing disposed separately at a long distance from the rear wheel in order to steer the rear wheel, the system has still another drawback that only a very small steering angle can be provided from the operating amount of the actuator.